Desirable properties for photographic silver halide recording material include high sensitivity (i.e., speed), low granularity, and high sharpness. With respect to sharpness, the recording material should enable faithful reproduction and display of both coarse and fine details of the original scene. This combination of sharpness performance has proven difficult to achieve in practice, especially in combination with high sensitivity and low granularity. A general description of the nature of this problem may be found in T. H. James, Ed., "The Theory of the Photographic Process," Macmillan, New York, 1977 and, in particular, at Chapter 20 of this text, pages 578-591, entitled "Optical Properties of the Photographic Emulsion" by J. Gasper and J. J. DePalma.
One method of improving sharpness, disclosed at U.S. Pat. No. 4,312,941 and at U.S. Pat. No. 4,391,884, involves the incorporation of a spatially fixed absorber dye in a film layer between the exposing light source and a layer comprising a conventional grain light sensitive silver halide emulsion. In these disclosures, the absorber dye is held spatially fixed either by means of a ballast group or by means of a mordanting material incorporated at a specified position in the film structure. Use of this spatial arrangement of absorber dye and emulsion reduces front-surface halation effects and improves sharpness, but at the expense of grain and speed.
U.S. Pat. No. 4,439,520, inter alia, discloses the utility of sensitized high aspect ratio silver halide emulsions for use in light sensitive materials and processes. These high aspect ratio silver halide emulsions, herein known as tabular grain emulsions, differ from conventional grain emulsions in many characteristics. One differential characteristic is the relationship between the emulsion grain thickness and the emulsion grain equivalent circular diameter. Conventional grain emulsions tend to be isotropic in shape and, when incorporated in a film structure, tend to be randomly oriented within a particular layer. Tabular grain emulsions however, tend to be anisotropic in shape and, when incorporated in a film structure, tend to align such that their major axis parallels the plane of the film base. This degree of anisotropicity is know as the emulsion aspect ratio (AR), typically defined as the ratio of the emulsion grain equivalent circular diameter divided by the emulsion grain thickness. The ability to control emulsion grain thickness and alignment within a film structure can enable the realization of otherwise unattainable degrees of recording material performance.
The optical properties of photographic recording materials incorporating tabular grain emulsions are described in great detail at "Research Disclosure", No. 25330, May, 1985, as are methodologies of specifying particular arrangements of tabular grain emulsions within a film structure and of specifying particular tabular grain emulsion thicknesses so as to enable the attainment of specifically desired properties, such as speed or sharpness in underlying or overlying emulsion layers.
These methods may not prove to be wholly satisfactory. U.S. Pat. No. 4,740,454, for example, discloses that although high frequency sharpness may be attained by the appropriate choice of tabular grain emulsion thickness and placement, this can be at the cost of low frequency sharpness. The term "high frequency sharpness" generally relates to the appearance of fine detail in a scene reproduction, while the term "low frequency sharpness" generally relates to the appearance of clarity or "snap" in scene reproduction. It is understood that the terms "high frequency sharpness" and "low frequency sharpness" are qualitative in nature and that both image spatial frequency, expressed as cycles/mm in the film plane, and the image magnification employed in producing a reproduction must be taken into account when specifying such terms. This publication discloses that both high frequency and low frequency sharpness may be simultaneously improved by the incorporation of specific mercaptothiadiazole compounds in combination with tabular grain silver halide emulsions. This practice may not be wholly satisfactory since the incorporation of such silver ion ligands can lead to deleterious effects on film speed and film keeping properties.
In related areas, U.S. Pat. Nos. 4,746,600 and 4,855,220 disclose that large degrees of sharpness can be attained by combining spatially fixed absorber dyes and Development Inhibitor Releasing Compounds (DIR Compounds) in a photographic silver halide recording material. The spatially fixed absorber dye is positioned between an emulsion containing layer and the exposing light source. The materials described in these disclosures incorporate either conventional grain silver halide emulsions or low aspect ratio tabular grain silver halide emulsions. U.S. Pat. No. 5,308,747 discloses that the use of positioned absorber dyes in a layer between an exposing source and a layer comprising high aspect ratio tabular grain silver halide emulsions results in even larger sharpness improvements. U.S. Pat. No. 5,399,469 discloses that the use of spatially fixed absorber dyes in a less sensitive layer positioned below a more sensitive layer sensitized to the same region of the electromagnetic spectrum which is closer to an exposure source provides improved image sharpness without compromising photographic sensitivity.
In a further related area, U.S. Pat. No. 4,833,069 discloses that large degrees of sharpness can be attained by simultaneously controlling total imaging layer thickness to between 5 and 18 microns and incorporating large quantities, between 15 and 80 mol % of colored cyan dye-forming couplers, known also in the art as cyan dye-forming color masking couplers. This method may not be wholly satisfactory since the use of excessive quantities of color masking couplers can lead to inferior color rendition by over-correcting the color reproduction through excessive use of the masking function.
In yet another related area, U.S. Pat. No. 4,956,269 discloses that color reversal silver halide photographic materials incorporating tabular grain silver halide emulsions can show improved sharpness when the red and/or green sensitive layers of the material incorporates a quantity of absorber dye sufficient to reduce the speed of that layer by at least 20%, when the total imaging layer thickness is less than 16 microns and when the swell ratio of the film is greater than 1.25. The materials described in this disclosure incorporate intermediate aspect ratio (AR&lt;9.0) tabular grain silver halide emulsions. U.S. Pat. No. 5,395,744 discloses that the use of distributed absorber dyes in a color photographic negative material comprising high aspect ratio tabular grain silver halide emulsions and development inhibitor releasing couplers results in even larger sharpness improvements. U.S. Pat. No. 5,283,164 discloses the use of sufficient red absorbing dye in a color negative duplicating film comprising fine grain silver halide emulsion to closely match the acutance of the red and green color records.
Color negative silver halide photographic recording materials incorporating quantities of distributed dye sufficient to reduce the speed of each color record by about 50% have been commercially available for many years. Additionally, it has been common practice in the photographic art to commercially provide silver halide photographic recording materials incorporating conventional grain and/or tabular grain silver halide emulsions in combination with soluble dyes sufficient to reduce the speed of a color record by about 10% for purposes related to ease of manufacture. Likewise, color negative silver halide photographic materials incorporating high aspect ratio tabular grain silver halide emulsion with an average grain thickness of circa 0.11 and 0.14 microns in an intermediately positioned layer have been commercially available for many years.
Color difference screen matte photography has long been used in the special effects community for compositing two or more separate images. In such procedures, a subject is typically photographed on color negative film in front of a uniformly colored background screen, the photographic subject image is separated from the uniform background based upon color difference, and the subject image is then superimposed, or composited, with a desired background scene. The procedure may be repeated to composite multiple subject images in a single scene. The majority of this compositing work is now done by first digitizing the color negative film images on commercial film scanners and subsequently applying software algorithms to separate the principal subject from the uniformly colored (e.g., blue or green) matte background (for example, see "Blue Screen/Green Screen 101", American Cinematographer, December 1996, pp. 91-98). The separated subject image information may then be digitally composited with a desired background scene.
Blue screen and green screen backgrounds are most commonly used for color difference screen matte photography. Use of such blue screen and green screen backgrounds (as well as black screen backgrounds which also provide little red light exposure) with conventional color negative films, however, has been hampered by a particular deficiency in the resulting processed film original images, namely the existence of a pronounced cyan dye fringe observed in the red color record of the color negative film around the border between the foreground objects and the matte background which is not easily removed with digital software algorithms. Images exhibiting such fringe artifact which are to be digitized for compositing work accordingly must have the fringe removed painstakingly by rotoscoping techniques. Such red color record fringe problem has been found to appear in films which otherwise exhibit good red record image sharpness or acutance (e.g., relatively high conventional red Modulation Transfer Function, or MTF values measured using 60% or lower input modulation) for conventional scene (i.e., non-blue screen, green screen, or black screen) exposures. As such, conventional MTF values have been found to be an inadequate predictor of a films propensity to exhibit the red fringe problem.
Photographers and cinematographers generally desire the noise level in their images to be as low as possible. To minimize image noise in color negative films, cinematographers strive to use the slowest, finest grain stocks that lighting conditions permit. Unfortunately, in many circumstances lighting conditions cannot be altered, either because of the subject material or location constraints. The cinematographer has no choice but to use relatively more sensitive, albeit noisier, film stocks. Medium and high speed color negative stocks are often used in these applications, with use of film speeds of EI 200 and greater often being preferred. Additionally, blue screen and green screen color difference matte/subject separation algorithms are based on identifying colors of specific value. Accordingly, there is an added desire to work with origination films that exhibit low blue and green image noise (i.e., minimal granularity) for such applications, which property is typically not consistent with high sharpness.